Population
• number of individuals of a species in a
defined place and time.
10 Feb. 2009 Populations.ppt 1
5.3.1 Changes in populations
• ΔN = +B +I –D –E
+B = natality (the number of births)
+I = immigrants (immigration rate)
– D = deaths (death rate)
– E = emigrants (emigration rate)
(For many [most] natural populations I and E
are minimal.)
10 Feb. 2009 Populations.ppt 2
5.3.2: S-Shaped Population Growth Curve
5.3.3-Explain the reasons for the
exponential growth phase
• Plentiful resources (food, light, space, etc.)
• Little to no competition
• Abiotic conditions favorable (temp.,
dissolved oxygen, soil, etc.)
• Little to no predation or disease
• CAN THIS GO ON FOREVER???????
NO! 5.3.3-Explain the reasons
for the transitional phase
• Increasing competition between individuals
in the population (which type of
competition is this?)
• Predation increases (predators attracted to
growing food source)
• Disease spreads more easily due to a higher
density of individuals
5.3.4-Explain the reasons for the
plateau phase
• Resources and/or space become limited
(food supply, light, water)
• Build up of waste (excrement, carbon
dioxide)
• Predation
• Disease
Carrying Capacity
- The plateau phase defines the carrying
capacity
- Defined as the number of individuals that
the habitat can support
- It is not a constant, it fluctuates with
changing conditions (food availability,
climate, time of the year, etc.)
G.5.1 Distinguish between r and k strategies
Life History trait r-adapted, K-adapted,
Opportunistic Equilibrium
Offspring Many, small (high r) Fewer, large (low r)
Offspring survival Low High
Parental care Rare Common
Reproductive age Early Later
Reproduction Once Many times
Habitat Unstable, temporary Stable, permanent
Population regulation Density independent Density dependent
Population fluctuation Fluctuates greatly Stable near K
Survivorship Curve
K-strategists
R-strategists
Make a list of examples of organisms
that employ each strategy
R-Strategists K-Strategists
G.5.2-Discuss environmental
conditions that would favor r-
strategies or k-strategies
• Large environmental changes favor r-
strategists due to their immense number
offspring
• With so many offspring, a few are likely to
survive even in changed conditions
• Ecological disruptions such as natural
disasters or succession favor highly
adaptable organisms  higher degree of
variation (have many offspring)
K-strategists favor stable
environments due to…..
• their long gestation period
• High degree of parental care (example:
nursing mothers require more food)
• Only a few offspring, if they all die the line
will not continue
G.5.3- Describe how to estimate
population size with mark-
capture-release method
• Mark all the individuals in the population that you
find in one area
• Wait
• In the same area, catch as many as you can again
and mark any individuals that are not already
marked
• The proportion of marked to unmarked individuals
in the second sample is the same as the proportion
of the originally marked individuals to the whole
population
• Repeat the method at least five times
Capture mark release Equation:
• n1= number marked in first sample
• n2=total number caught in second sample
• n3= number marked in second sample
• N= size of the whole population
n3 = n1 N = n1 x n2
OR
n2 N n3
G.5.4 Describe methods used to
estimate the size of commercial
fish stocks
• Gather information from fishers (number and
kinds, questionnaires, logbooks)
• Use research vessels to:
– Cast nets and sample many locations randomly
– Echo sounders (sometimes even the species can be
detected), trawling is used to verify
– Age of the fish can be indicated by counting the rings
on their ear bones
– Tagging fish (similar to mark-capture-release method)
– Using mathematical models
G.5.5-The concept of maximum
sustainable yield in fish stocks
• The highest proportion of fish that can be
removed without jeopardizing this
maximum yield in the future.
• If there are not enough adults, there will not
be enough offspring
• Often females are protected over males for
this reason (example: Dungeness crabs)
G.5.6 International measures that
would promote fish conservation
• All seafood species have declined by 29%
(2006)
• If this continues, there will be no more
commercial fishing by 2048
• Some stocks have already declined by much
more than the above average (North sea cod
by 75%, North Atlantic Haddock by 50% in
one year!)
G.5.6 International measures that
would promote fish conservation
• Regulate trawling (lots of by-catch)
• Rebuild depleted populations (fish farms,
protecting spawning grounds)
• Eliminate wasteful fishing practices (mostly nets)
• Enact and enforce catch limits
• Provide funds for research on populations
• Encourage scientist-fisher relationships
• Establish marine reserves (no fishing there!)